[redleader]

Originally Posted by HAL-9000

I think you can condense CO2 in a single phase system.

If you live at the south pole, and its winter, sure. Otherwise, given taht its critical temperature is a few degrees above room temp, you have a problem.

I am aware the pressure is 700psi

I'd say more like 1000 psi.

, but you're seeing this refrigerant (R744 apparently) being implemented in cars for the express purpose of getting rid of other refrigierants due to the relative greenhouse gas/toxic issues of other refrigerants such as R134a. European regulations are set to ban these other refrigerants from being legal in autos there, so there is some considerable work being done on compact, portable implementations of this technology from the compressor side.

I'm not saying its impossible to condense CO2, I'm saying you won't be able to get a compressor that will do it. Simple as that. And I really really doubt Europe is using straight 744 in cars. Given that its critical temperature around room temp, that would make it pretty useless (who wants an AC that only works during the winter and costs a few grand?). They'll probably develope some blend with 10 or 20 percent CO2, and some other gases making up that rest.

I am not sure how intense of a power draw will be going on with such a system, but at least 1 HP I would guestimate, probably more.

Power has nothing to do with this, and using a larger compressor will not address the condensing pressure issue.

Could you get away with a single stage system.... if they are doing it in autos, I would assume so

Could you deal with a cascade system.... yes, though it would be a pain.

Search on google. People have been building lots of cascaded systems with CO2. Thats not special. The difference is, they condense it at -40C because its not a first stage gas.

Assuming all these other issues are taken care of, one issue remains: namely, how do you turn the thing on?

If you try and turn the processor on after the thing has reached "operating temperature" you will thermally shock that processor, and probably crack the die in the process. Obviously, if you turn the processor on first, it will be dead before the coolant system will matter. Maybe a speedstepping proc would make a difference if its supported, but the processor won't last long getting cycled up and down like that anyways. This would even matter between running at idle and max is the gradient were steep enough. The third option is a gradual rise in either the cooling system capacity, or the processor speed. While that idea could be made to work with a ton of money and work, it doesn't matter.

No matter what you do you end up with a rig like what I see posted all the time at xtremesystems.org. Basically a top fuel dragster that can't do anything more useful than post 3D Mark scores. Not what I'm after for sure.

You're not going to thermally shock a processor by slowly cooling it and then powering it on. The limitation here is how well your system works and for how long it can keep running.